1. Field of the Invention
The present invention relates to a belt moving device for controllably moving a belt and more particularly to a belt moving device capable of accurately controlling the position of an intermediate image transfer belt included in a color image forming apparatus, and an image forming apparatus including the same.
2. Description of the Background Art
An intermediate image transfer belt included in a color printer or similar color image forming apparatus has its position controlled by a belt moving device. The problem with a conventional belt moving device is that because it controls the position of the belt on a speed basis, positional deviation increases with the elapse of time. Particularly, in a color copier configured to sequentially transfer a black, a yellow, a magenta and a cyan toner image to the belt one above the other, the above positional deviation results in color misregister. The color misregister cannot be canceled when the positional deviation is derived from, e.g., disturbance. More specifically, while position control allows, even when misregister occurs, the belt to follow a target position later, speed control cannot do so. This will be described more specifically later with reference to the accompanying drawings.
Further, as for a drive roller for driving the belt, speed control is effective for a frequency as low as the rotation period of the roller, but cannot cope with banding or similar speed variation whose frequency is high.
Technologies relating to the present invention are disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 6-263281, 10-232566, 2001-5363 and 2002-258574.